The present invention relates to a golf club head.
In recent years, the golf club heads have achieved weight reduction by reducing face thickness. In addition, the golf club heads are also increased in the restitution coefficient at the face thereby achieving enhanced carry performance for carrying the ball over a greater distance.
In general, the golf club head exhibits the maximum value of restitution coefficient at the face center, the restitution coefficient progressively being decreased from the face center toward a circumference of the face.
It has been a conventional practice to increase the restitution coefficient at the face center, so as to maintain relatively high restitution coefficients at the other portions than the face center. Even when an impact point is deviated from the face center, therefore, the head is not extremely lowered in the carry performance. However, a worldwide trend is toward prohibition of the use of golf clubs having high restitution coefficients. For instance, the US Golf Association (U.S.G.A.) and the Royal and Ancient Golf Club of St. Andrews (R&A) specify the upper limit of the restitution coefficient of the golf club heads. This makes it difficult to maintain the high restitution coefficients at the other portions than the face center by increasing the restitution coefficient at the face center, as practiced in the conventional heads. Hence, a fear exists that the golf club head may be extremely lowered in the carry performance when the impact point is deviated from the face center.
Because of the above situations, there is a demand for a golf club head in which relatively high restitution coefficients are evenly distributed in a wide area or from the face center toward the circumference of the face. Such a face design lessens the drop of restitution coefficient even when the impact point is deviated from the face center. Hence, the face design can ensure a consistently high carry performance and besides, clear the restriction on the restitution coefficient.
In this connection, a proposal has been made to expand a sweet spot by forming a rib on a face backside in an annular shape about the face center, whereby the face may be increased in an area having a relatively high restitution coefficient (see, for example, Japanese Unexamined Patent Publication No. 2004-533894 (FIG. 1 and FIG. 2)).
However, even the golf club head disclosed in the above patent publication cannot achieve the consistent carry performance because there may be a case where the area having the relatively high restitution coefficient is not large enough, and because the other face portions than the above area suffer a significant drop of restitution coefficient. On this account, there has been a strong demand for a technique which is applied to the golf club head for permitting the head face to attain the high restitution coefficient evenly distributed across a wide area such that the drop of restitution coefficient may be lessened even when the ball impact point is deviated from the face center.